Accepted theory on blackleg in potatoes challenged

The widely held theory that varietal susceptibility is a key factor in the spread of blackleg could be wrong.

That was one of the findings in a survey of all 28 specialist Pre Basic (PB) seed growers in Scotland.

Gerry Saddler of Science and Advice for Scottish Agriculture (Sasa) told delegates to the Crop Protection in Northern Britain Conference in Dundee that a study of field inspection results did not back up the notion that some varieties, particularly those of Dutch origin, were soft targets for the bacterial disease.

“It might seem that way but once we had adjusted the results to take account of the areas grown of each variety there was little difference between UK and continental varieties and old and new varieties from any source, “Dr Saddler said.

He and colleagues conducted the survey by means of in depth interviews with growers, many of whom had more than 20 years’ experience.

The process had been prompted by a spike in seed certification rejections in 2011 and 2012.

“Blackleg levels then were at a level we hadn’t seen for 20 years despite advances in storage practice,” he said.

“It was clear from the survey that increasing economic pressures are being felt by most PB growers, with the need to increase business size and complexity an almost inevitable consequence.

“There was tacit recognition that these factors could be contributing to the spread of blackleg as attention to detail was an almost inevitable casualty under such circumstances.”

The survey also showed that paying attention to drying and curing of the harvested crop was felt to be most important.

Years when this was difficult often led to blackleg problems in the following crop.

The survey is to be widened to include other seed growers this spring using an online format.

The PB growers also believed the loss of sulphuric acid as a fast-acting dessiccant had led to increased problems with tubers becoming more readily infected when slower methods of haulm destruction were used.

Blackleg is a bacterial disease that causes the leaves to wilt and the stems to blacken.